It is often desirable to display a stop action or slow motion view of a heart over one or several oscillation cycles of the heart. This can be done using a cine loop that records real time acoustical imaging signals, either digitally or on magnetic tape. The images are then played back slowly in sequence to simulate slow motion of the heart. The cine loop apparatus is usually complex and expensive and must repeat the recorded cycle in order to simulate continuous slow motion.
Apparatus for measuring and displaying the time lapse between the time of a heart beat, recorded electrocardiographically, and a corresponding pulse produced at a periphery of a limb of the body, is disclosed by Phelps in U.S. Pat. No. 3,734,086. The apparatus measures pulse propagation time from the heart to an extremity of the body and uses the same operational position in the heart cycle for each time lapse measurement. Images of the heart at different positions in the heart cycle are not formed.
Apparatus for measuring the time interval between two consecutive heartbeats and for counting the number of such time intervals that are of substantially equal length is disclosed in U.S. Pat. No. 4,027,663, issued to Fischler et al., in U.S. Pat. No. 4,346,718, issued to Morris, in U.S. Pat. No. 4,364,397, issued to Citron et al., and in U.S. Pat. No. 4,513,753, issued to Tabata et al. These patents do not disclose formation of an image of the heart at different positions in the heart cycle. The Citron et al. patent also monitors the length of the period of the heart primary oscillation cycle to determine whether this period indicates that a regular rhythm is present.
Scott, in U.S. Pat. No. 4,271,437, discloses a time lapse videotape editor and controller that permits formation of images of a scene at a desired frequency for a predetermined time interval.
In U.S. Pat. No. 4,263,548 issued to Carlson et al., apparatus is disclosed that accepts or measures a first time interval of length .DELTA.t, then immediately generates a second time interval of length .DELTA.t/n where n is apparently an integer. At the end of this second time interval a strobe pulse is generated that may be used to turn on certain analog voltage, current or resistance measuring circuits. The patent does not disclose or suggest how, if at all, the apparatus might be used to time repetitive measurements on cyclic phenomena.
Animated illustration, using photographs of a plurality of drawings showing an object in motion at a sequence of times that are spaced apart by a small time interval to give the appearance of smooth motion, is disclosed by Tamura in U.S. Pat. No. 4,346,403. The photographs are stored in an image storage device and are redisplayed individually to permit an artist to produce "in-between" drawings that show the moving object(s) at intermediate times that do not coincide with the image formation times.
In U.S. Pat. No. 4,710,717, Pelc et al. disclose a method for fast scan cinematographic imaging of a heart cycle using nuclear magnetic resonance ("NMR") imaging techniques. This method contemplates formation of more than one image during a heart cycle because the NMR process requires considerable time to form images. Thus, the technique probably does not extend to formation of images of a heart over an arbitrary number of oscillation cycles of the heart.
What is needed here is a technique that is inexpensive and relatively simple to apply and that allows formation of a sequence of images of the heart at different positions throughout a heart oscillation cycle, where the image formation period may extend over as many oscillation cycles as desired and may be displayed in real time.